1. Field of Invention
This invention relates to aqueous anionic silicone emulsions which cure to elastomers upon removal of the water and which contain a tin compound as a catalyst.
Background Information
A group of aqueous anionic silicone emulsions have been developed which yield elastomers upon removal of the water from the emulsion. Some of these compositions contain a tin compound as a catalyst. It has now been found that the properties of such emulsions containing a tin compound vary as the composition ages. In particular, the elongation of the elastomer produced by removing the water tends to decrease as the emulsion ages after its manufacture.
In U.S. Pat. No. 4,221,688, issued Sept. 9, 1980, Johnson et al. teach a silicone emulsion having a dispersed phase of an anionically stabilized hydroxylated polydiorganosiloxane and a colloidal silica and a continuous phase of water in which the pH is 9 to 11.5. Upon removal of the water at ambient conditions, an elastomeric product such as a film or coating is produced. A period of time is required during which the polydiorganosiloxane and colloidal silica interact to form a composition which gives an elastomer upon removal of the water. The required time is lowered from a period such as 5 months to a period of a few days by the use of an organic tin compound, preferably a diorganotindicarboxylate.
In U.S. Pat. No. 4,244,849, issued Jan. 13, 1981, Saam teaches an aqueous silicone emulsion which provides an elastomeric product upon removal of the water under ambient conditions. The emulsion comprises a continuous water phase and an anionically stabilized dispersed silicone phase which is a graft copolymer of a hydroxyl endblocked polydiorganosiloxane and an alkali metal silicate. An organic tin compound can be employed to accelerate the formation of the graft copolymer.